The rapid decrease in viscosity of liquids with increasing temperature on polymer concentration is well-known. Ideally, for many applications (automobile lubricants, etc.) it would be desirable to solve this problem so that viscosity would be insensitive to temperature or polymer level. Alternatively, it might be desirable to provide liquid systems whose viscosities actually increase with temperature or increase as polymer level is decreased. It is true that with selected polymeric additives it has been possible to reduce substantially the viscosity change with temperature which does occur with most oils and similar systems. These polymer additives, known as viscosity index improvers (or V.I. improvers) are generally high molecular weight polymers.
The way in which these additives function can be summarized very briefly. In effect, they perform two functions, i.e., thickening, which merely increases fluid viscosity; and Viscosity Index (V.I.) improvement, which corresponds to limited thickening at ambient temperatures and a correspondingly greater thickening at elevated temperatures. This can be accomplished by utilizing a polymeric additive which is poorly solvated by the liquid at ambient temperatures; however, at elevated temperatures the polymer is more highly solvated, such that the polymer expands and is a relatively more effective thickener.
While these V.I. Improvers have proven successful commercially, it is important to note that their effect at reducing viscosity changes with temperatures is rather mild. For a typical base oil containing a suitable V.I. Improver the kinematic viscosity will still decrease by a factor of from 5 to 10 as the temperature increases from 30.degree. C. to 100.degree. C. Obviously, if it is desired to hold the viscosity roughly constant with such temperature changes current technology has not offered an appropriate additive system. Alternatively, it if is desired to hold viscosity reasonably constant as the polymer concentration is decreased conventional wisdom has not previously offered that option.
U.S. Pat. No. 3,396,136 describes how copolymers of alkenyl aromatic sulfonic acids, when properly neutralized, can be employed as thickeners for nonpolar solvents. Those metal sulfonate systems have been shown to be very effective; however, when employed as to component systems (i.e., ionic polymer plus non-polar solvent) the variation of viscosity with increased temperature is very conventional and predictable. That is, the solution viscosity decreases markedly as temperature is increased.
U.S. Pat. No. 3,396,136 further teaches "in situ" neutralization of the sulfonic acid polymer which, under some conditions, can result in the availability of a small amount of polar cosolvent, i.e., a solvent for the sulfonate groups, about equal in amount to the amount of sulfonate groups which are present. This amount of polar cosolvent is not within the limits of the instant invention, which only optionally requires amounts of the third component (which interacts with the ionomeric groups of the ionomer copolymer) at levels which range from 10 to 600 times the molar equivalent of ionic groups. This level of cosolvent is about one to two orders of magnitude or more higher than employed in the cited art. In addition, the cited patent is restricted to aromatic sulfonate polymers. The instant invention describes other polymers, such as sulfonated ethylene propylene terpolymers, sulfonated Butyl, etc., which are a portion of the polymer complex.
U.S. Pat. No. 3,366,430 teaches the gelling of organic liquids by the interaction of polar "associative bonds" which includes hydrogen bonding and "ionic cross-linking". Again, this patent specifies that two components are necessary--the associating polymer (or polymers in some cases) and the non-polar organic liquid. There is no mention of a third polar cosolvent except to point out that such polar liquids should not be present. Specifically, this patent states (at column 2, line 7) that the hydrocarbon liquids to which this invention is to be applied should not contain a substantial portion of a miscible protolytic liquid, such as methanol. It is clear that the language of this patent limits this invention to gels and further that any amount of polar liquids which are present to an extent where they disrupt those gels are undesirable. The instant invention is distinct from that cited in that amounts of such polar compounds as will break up gel at ambient conditions are often desirable and, in fact, the preferred state is free of any said gel at ambient temperatures.
U.S. Pat. No. 3,679,382 teaches the thickening of aliphatic hydrocarbons with synthetic organic polymers which contain olefinically unsaturated copolymerizable acids, amides, hydroxyacrylic esters, sulfonic acids, etc. It is emphasized in this patent (at column 3, line 72) that it is critical that in the preparation of such polymers no surface active agent, catalyst or other additive be employed which introduces a metallic ion into the system. Therefore, it is preferred to employ ammonium or amine salts. It is clear that this invention (U.S. Pat. No. 3,679,382) specifically precludes the use of metallic counterions and is directed towards amine or ammonium derivatives. Metallic counterions are very effective in the instant invention. Finally, this cited patent does describe (at column 7, lines 13-19) that the addition of alcohols will reduce the viscosity of the thickened hydrocarbon and alter flow characteristics thereof.